Certain treatments may require the temporary or permanent interruption or modification of selected nerve function. One exemplary treatment is renal nerve ablation, which is sometimes used to treat conditions related to congestive heart failure or hypertension. The kidneys produce a sympathetic response to congestive heart failure, which, among other effects, increases the undesired retention of water and/or sodium. Ablating some of the nerves running to the kidneys may reduce or eliminate this sympathetic function, which may provide a corresponding reduction in the associated undesired symptoms.
Many nerves (and nervous tissue such as brain tissue), including renal nerves, run along the walls of or in close proximity to blood vessels and thus can be accessed intravascularly through the walls of the blood vessels. In some instances, it may be desirable to ablate perivascular nerves using ultrasonic energy. In other instances, the perivascular nerves may be ablated by other means including application of thermal, radiofrequency, laser, microwave, and other related energy sources to the target region. Ultrasound transducers may dissipate some energy as heat into the blood and surrounding tissue as well as causing the ultrasound transducers to become hot. This may result in blood damage, clotting, and/or protein fouling of the transducer among other undesirable side effects. In some instances, overheating of the ultrasound transducer may result in the failure of the transducers.